Optical burst switching (OBS) is an optical switching technology newly developed in recent years. The basic principle of the OBS is to transfer the data and control information respectively through independent channels. An edge node of OBS networks assembles several IP packets having the same features, such as the same destinations and the same service levels into one burst packet. The control information in the form of packet sent earlier than the burst packet, referred to as a control packet, is used to reserve bandwidth resources for the burst packet at every intermediate node in a route to a destination node, so that the burst packet sent after the corresponding control packet remains in the optical domain all the time during the network transmission. Thus, the problem that the packet headers are processed one by one during the packet switching is avoided. At the same time, the demands for the optical buffer at the intermediate nodes of the network may be avoided or reduced.
A data switching network often needs to carry various different services. Some of them have high Quality of Service (QoS) requirements and economic or social values. The cut-down of these services due to network failures often causes great loss. Therefore, services superior to ordinary services must be provided for these services of higher authority levels. The service protection method against network failures is the most basic manner. Among all the protection manners against network failures, a 1+1 service protection is capable of transferring services simultaneously on two risk-independent routes and selecting the arrived data stream at a receiving end, thus reducing the impact of a single point network failure on the services to the minimum. The 1+1 service protection adopted in the OBS networks can eliminate the influence of the single point failure in the networks on the services carried by the network, provide differentiated services, and enhance the reliability of the transfer of important services. FIG. 1 shows a schematic diagram illustrating 1+1 service protection in OBS networks.
In a solution of the prior art, a conventional multi-protocol label switching (MPLS) 1+1 service protection strategy is introduced into the OBS network. The solution mainly includes the following processes. When establishing a session between a service source and a sink node, resources are reserved simultaneously on two risk-independent routes. A burst packet bearing service is replicated, in an appropriate manner, into two packets with the same content and number and the two burst packets are placed on the two routes, respectively, for transfer. Regarding a burst packet placed on either route for transfer, the sequence number of the burst packet is added in its corresponding control packet sent earlier than the burst packet. Moreover, a receiving window of the sequence number of the burst packet having a width of L is disposed at an intersection node where the two routes converge together. The value of L should be great than the maximum number of burst packets that may possibly be continuously lost on a single route. That is, when the network operates normally, the number of the packets that are continuously lost on a certain route from the source node to the sink node is smaller than L. Then, the receiving window filters the burst packets at the intersection node where the two routes converge together, based on the following principle. If the number (set to be N) of the burst packet carried by a control packet reaching the intersection node falls in the range of the current receiving window, this corresponding burst packet will be received, and meanwhile, the receiving window proceeds to the receiving range [N+1, N+L]; otherwise, this corresponding burst packet will be discarded.
FIG. 2 shows a schematic diagram illustrating conventional processes of selecting a packet by a receiving window at an intersection node, according to the aforementioned MPLS 1+1 service protection strategy. The processes are briefly described as follows. In FIG. 2, the receiving range of the receiving window is [1, L] initially. A packet 1 transferred through a route 1 first reaches the intersection node and is received (the sequence number of the packet 1 is within [1, L]), and meanwhile, the receiving range of the receiving window proceeds to [2, L+1]. Consequently, the packet 1 transferred through a route 2 reaching the intersection node later is discarded. Then, a packet 2, transferred through the route 1, reaches the intersection node earlier than the packet 2, transferred through the route 2, and is received, and, hence, the receiving range of the receiving window proceeds to [3, L+2]. Consequently, the packet 2 transferred through the route 2 reaching the intersection node later is discarded. After that, a packet 3 transferred through the route 1 fails to reach the intersection node for some reason (e.g. a failure of the route 1 occurs, or the like), and the packet 3 transferred through the route 2 reaches the intersection node and is received, and, hence, the receiving range of the receiving window proceeds to [4, L+3]. Thereafter, a packet 4 transferred through both the routes 1 and 2 fails to reach the intersection node. Then, a packet 5 transferred through the route 1 fails to reach the intersection node, and the packet 5 transferred through the route 2 reaches the intersection node and is received, and, hence, the receiving range of the receiving window proceeds to [6, L+5], and so forth.
The inventor discovers at least the following deficiencies of the aforementioned solution of the 1+1 service protection in the OBS networks of the prior art.
1. Since the OBS node cannot sufficiently delay the burst packet, if an end-to-end time delay difference between two risk-independent routes is too large, the function of the above 1+1 service protection solution cannot fully exerted. Therefore, applications of the above solution are restricted in a network with a large coverage area.
2. In the OBS networks, since the optical buffer is insufficient, the packet loss ratio of the burst packet is always far greater than that in the traditional electrical switching network. When data packets bearing some services are simultaneously transferred through two different routes, the best way is to utilize the characteristic that the packet loss ratios of the two routes are independent from each other, so as to reduce the packet loss ratio of the entire service. However, the above 1+1 protection solution obviously cannot achieve this. For example, when a propagation time delay difference between the two risk-independent routes is larger than a time difference between two burst packets sent from a service source node, the packet loss ratio of the above protection solution is approximately the packet loss ratio of the shorter route.
3. During the transfer of the burst packets, the burst packets may undergo a wavelength transformation, delay, and other processes at each of the nodes, so as to avoid the burst packet collision, and may probably undergo a shaping, amplification, and other processes, so as to optimize the signal quality. Therefore, at the sink node of a service, the signal qualities of multiple burst packets transferred through the same route are not definitely the same, and the signal quality of the burst packets transferred through the shorter route is not definitely better than that of the burst packets transferred through the longer route. Therefore, it is of important practical significance to select the burst packet having a better signal quality from two burst packets with the same content transferred through different routes, in order to provide better QoS for the services of higher service levels. However, the above 1+1 protection solution can only ensure that the service will not be cut down when a network failure occurs and is incapable of filtering, with respect to qualities, the optical signals transferred through the two different routes when the network operates normally.